Over the last few years, there has been a tremendous growth in the use of multiple-beam antenna systems for satellite communications. For example, multiple-beam antennas are currently being used for direct-broadcast satellites (DBS), personal communication satellites (PCS), military communication satellites, and high-speed Internet applications. These antennas provide mostly contiguous coverage over a specified field of view on Earth by using high-gain multiple spot beams for downlink (satellite-to-ground) and uplink (ground-to-satellite) coverage.
Fixed Satellite Service (FSS) and Broadcast Satellite Service (BSS) payloads require that the spectral resource use be optimized, in order to enable several satellite operators to efficiently share a limited frequency spectrum. For satellite systems that require multiple spot beams to contiguously cover a large geographic coverage region, key performance parameters include the frequency-reuse factor and the co-polar isolation (C/I). For the downlink coverage, the co-polar isolation is usually more critical than for the uplink coverage. This parameter may be defined as the ratio of the co-polar directivity of the beam of interest to the combined directivity interference of all the beams that reuse the same frequency and is obtained by adding all the interferers, in power over the beam of interest.
To cover a large number of cells in the coverage region, conventional satellite systems utilize multiple-cell frequency-reuse schemes with a fixed number of cells using the same frequency channels. For example, a 4-cell frequency-reuse scheme or a 7-cell frequency-reuse scheme may be utilized. However, these known frequency-reuse schemes have some drawbacks. While the 4-cell frequency-reuse scheme provides a high system capacity and a high frequency-reuse factor, it has low C/I values. By contrast, the 7-cell frequency-reuse scheme limits the system capacity, but has better C/I values that makes the system inoperable. In addition, both these fixed-cell reuse schemes do not cater for non-uniform traffic demands based on geographic population of the coverage region. For example, the eastern and western regions of the Continental United States (CONUS) have higher spectral demand than the mountain and central regions.
Hence, there is a need for a multiple-beam antenna system supporting a hybrid frequency-reuse scheme that would provide a required system capacity with a sufficient co-polar isolation.